Your baby is growing -- he's now a tiny bundle about the size of a lima bean. He is well-cushioned in his uterine home, afloat in the clear "waters" of the ever-growing amniotic sac. Here, he can drift around freely, while still remaining attached to the placenta by the bungee-like umbilical cord. The placenta is busy processing nutrients from your bloodstream to nourish the embryo, while also disposing of waste produced by him.

At this point, the embryo's entire body is beginning to uncurl a bit, but its head is still very large in proportion to the rest of it. This will also be true after birth: a newborn's head makes up about a quarter of its length, while an adult's is only an eighth.

The esophagus, which brings food to the stomach, forms this week, and on either side of it, two buds that are the beginning of lungs. Imagine: it will be eight months until those lungs gulp their first breath of air.